In the SPIE 2016 Unconventional Imaging session, the authors laid out a breakthrough new theory for active array imaging that exploits the speckle return to generate a high-resolution picture of the target. Since then, we have pursued that theory even in long-range (&lt;1000-km) engagement scenarios and shown how we can obtain that high-resolution image of the target using only a few illuminators, or by using many illuminators. There is a trade of illuminators versus receivers, but many combinations provide the same synthetic aperture resolution. We will discuss that trade, along with the corresponding radiometric and speckle-imaging Signal-to-Noise Ratios (SNR) for geometries that can fit on relatively small aircraft, such as an Unmanned Aerial Vehicle (UAV). Furthermore, we have simulated the performance of the technique, and we have created a laboratory version of the approach that is able to obtain high-resolution speckle imagery. The principal results presented in this paper are the Signal to Noise Ratios (SNR) for both the radiometric and the speckle imaging portions of the problem, and the simulated results obtained for representative arrays.

In a recent paper [J. Opt. Soc. Am. A 33, 1931–1937 (2016)], the target-in-the-loop (TIL) phasing of an RF-modulated or multi-phase-dithered fiber laser array, fed by a linewidth-broadened master oscillator (MO) source, was investigated. It was found that TIL phasing was possible even on a target with scattering features separated by more than the MO’s coherence length as long as the received, backscattered irradiance changed with the array’s modulation or phase dither. To simplify the problem and gain insight into how temporal coherence affects TIL phasing, speckle and atmospheric turbulence were omitted from the analysis. Here, the scenario analyzed in the prior work is generalized by including speckle and turbulence. First, the key analytical result from the prior paper is reviewed. Simulations, including speckle and turbulence, are then performed to test whether the conclusions derived from that result hold under more realistic conditions.

In this paper, we present two analytic theories developed recently to predict the performance of an imaging system composed of a phased array illuminator and a set of receiver subapertures. The receiver need not coincide with the transmitter. The two theories have been documented separately (ref. 1, 2), and the reader can find more details there – the theories present the analytic phased array irradiance on target in the presence of piston errors, and the resulting speckle pattern-induced imaging noise. The principal results presented here are the Signal to Noise Ratios (SNR) for both the radiometric portion of the problem and the speckle imaging portion of the problem.

Scintillation and anisoplanatism significantly degrade a laser transmitter system or an imaging system when the optical field is required to propagate through deep turbulence. Here turbulence is defined as deep turbulence when the Rytov number is very much greater than 1 and the isoplanatic patch size is much smaller than λ/D, the diffraction limit. In this region a point beacon is of little use for imaging applications and a finite-sized beacon limits performance for both transmission and imaging because almost any finite-sized beacon is many isoplanatic patch sizes across and exhibits a significant level of beacon anisoplanatism. As a consequence, conventional adaptive optics techniques are of little value. To address this situation, five approaches are considered. These approaches include beacon deconvolution, Zernike tomography, gradient descent tomography (GDT), irradiance redistribution branch cut multiconjugate adaptive optics compensation, and minimum energy loss eigenfield propagation. GDT appears to have the most promise as it does not require a conventional wavefront sensor.

Anisoplanatism is a primary source of photometric and astrometric error in single-conjugate adaptive optics. We present initial results of a project to model the off-axis optical transfer function in the adaptive optics system at the Keck II telescope. The model currently accounts for the effects of atmospheric anisoplanatism in natural guide star observations. The model for the atmospheric contribution to the anisoplanatic transfer function uses contemporaneous MASS/ DIMM measurements. Here we present the results of a validation campaign using observations of naturally guided visual binary stars under varying conditions, parameterized by the <i>r</i><sub>0</sub> and &theta;<sub>0</sub> parameters of the C<sup>2</sup><sub>n</sub> atmospheric turbulence profile. We are working to construct a model of the instrumental field-dependent aberrations in the NIRC2 camera using an artificial source in the Nasmyth focal plane. We also discuss our plans to extend the work to laser guide star operation.

Adaptive optics (AO) is essential for many elements of the science case for the Thirty Meter Telescope (TMT). The
initial requirements for the observatory's facility AO system include diffraction-limited performance in the near IR, with
50 per cent sky coverage at the galactic pole. Point spread function uniformity and stability over a 30 arc sec field-ofview
are also required for precision photometry and astrometry. These capabilities will be achieved via an order 60&times;60
multi-conjugate AO system (NFIRAOS) with two deformable mirrors, six laser guide star wavefront sensors, and three
low-order, IR, natural guide star wavefront sensors within each client instrument. The associated laser guide star facility
(LGSF) will employ 150W of laser power at a wavelength of 589 nm to generate the six laser guide stars.
We provide an update on the progress in designing, modeling, and validating these systems and their components over
the last two years. This includes work on the layouts and detailed designs of NFIRAOS and the LGSF; fabrication and
test of a full-scale prototype tip/tilt stage (TTS); Conceptual Designs Studies for the real time controller (RTC) hardware
and algorithms; fabrication and test of the detectors for the
laser- and natural-guide star wavefront sensors; AO system
modeling and performance optimization; lab tests of wavefront sensing algorithms for use with elongated laser guide
stars; and high resolution LIDAR measurements of the mesospheric sodium layer. Further details may be found in
specific papers on each of these topics.

We present a model for MEMS deformable mirrors (DMs) that couples a 2-dimensional, linear 4th order partial
differential equation for the DM facesheet with linear spring models for the actuators. We estimate the
parameters in this model using the method of output least squares, and we demonstrate the effectiveness of this
approach with data from a 140-actuator MEMS test mirror produced at Boston University. A scheme for robust,
computationally efficient open-loop control, which is based on this model, is also presented.

In this paper, we provide an overview of the adaptive optics (AO) program for the Thirty Meter Telescope (TMT) project, including an update on requirements; the philosophical approach to developing an overall AO system architecture; the recently completed conceptual designs for facility and instrument AO systems; anticipated first light capabilities and upgrade options; and the hardware, software, and controls interfaces with the remainder of the observatory. Supporting work in AO component development, lab and field tests, and simulation and analysis is also discussed. Further detail on all of these subjects may be found in additional papers in this conference.

Achieving the science goals of TMT will require AO subsystems of unprecedented power and sophistication, including a
Real Time Controller (RTC) subsystem that will implement wavefront reconstruction and control algorithms for up to
four different laser guide star (LGS) AO systems. The requirements for the RTC represent a significant advance over the
current generation of astronomical AO control systems, both in terms of the wavefront reconstruction algorithms to be
employed and the new hardware approaches that will be required. Additionally, the number of active components
included in the AO systems and the complexity of their interactions will require a highly automated AO Sequencer that
will work in concert with the TMT Telescope and Instrument Sequencers. In this paper, we will describe the control and
software requirements for the whole AO system, and in particular for the RTC and the AO Sequencer. We will describe
the challenges involved in developing these systems and will present a conceptual design.

The estimation accuracy of wavefront sensors in strong scintillation is examined. Wave optical simulation is used to characterize the performance of several wavefront sensors in the absence of measurement noise. The estimation accuracy of a Schack-Hartmann sensor is shown to be poor in strong scintillation due primarily to the presence of branch points in the phase function. The estimation accuracy of a unit-shear, shearing interferometer is found to be significantly better than that of a Hartmann sensor in strong scintillation. The estimation accuracy of a phase shifting point diffraction interferometer is shown to be invariant with scintillation.

This paper describes the differential phase experiment (DPE) which formed a major part of the ABLE ACE suite of experiments conducted by the Air Force. The work described covers the rationale for the experiment, the basic experimental concept, the analysis of the differential phase, the optical and software design analysis, a discussion of the polarization scrambling characteristics of the optics, calibration of the equipment and a presentation of some of the major results of the data reduction effort to date. The DPE was a propagation experiment conducted between two aircraft flying at an altitude of 40,000 feet whose purpose was to measure the phase difference between two beams propagating at slightly different angels through the atmosphere. A four bin polarization interferometer was used to measure the differential phase. Due to the high level of scintillation that was presented branch points were present in the phase function. Rytov theory, wave optics simulation and the experimental measurements are in general agreement. Self consistency checks that were performed on the data indicate a high level of confidence in the results. Values of C<SUB>n</SUB><SUP>2</SUP> that are consistent with the measurements of the differential phase agree with simultaneous scintillometer measurement taken long the same path in levels of turbulence where the scintillometer is not saturated. These differential phase based C<SUB>n</SUB><SUP>2</SUP> estimates do not appear to saturate as is typical of scintillometer measurements and appear to extend the range over which high levels of C<SUB>n</SUB><SUP>2</SUP> can be estimated. In addition the differential phase and anisoplanatic Strehl computed from the data is consistent with Rytov theory and wave optics simulations.

It has been recognized for some time that full-order adaptive optics systems can provide considerable improvement in the performance of astronomical imaging systems. However, as 4-m-class telescopes become the standard for astronomical work it will become more difficult in terms of cost and complexity to build and operate full order AO systems, especially if one is interested in working in the visible. For the past several years, we have been developing simulation and analysis tools to study AO systems using laser guide stars. This analysis indicates that even low-order correction can provide improvements in image quality, especially when used in conjunction with computer post-processing algorithms.

We analyze the use of a single laser or natural guidestar to correct atmospheric distortion for a wide field of view (WFOV) imaging system. We concentrate on the absolute system limits without regard to radiometrics or compensation method by evaluating the best system OTF possible at field points in and beyond the isoplanatic patch. The improvement of OTF at mid- spatial frequencies is several decades over the non-corrected OTF even at field angles of one arc minute, and we conclude that post processing should be able to recover much more information in adaptive optics systems even at wide FOVs than uncompensated systems.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews